Recent vehicles including an opening/closing member such as a sunroof or a window regulator are generally provided with a safety mechanism. When the opening/closing member is operated by a motor, a safety mechanism detects trapping of an obstacle, and then stops a closing operation of the opening/closing member or moves the opening/closing member in a reverse direction, i.e. an opening direction, by driving the motor.
In known methods, the trapping of the obstacle is detected based on a rotational state of the motor. A rotation detecting sensor including a hall element and the like detects a change of the rotational state of the motor for driving the opening/closing member. The trapping is then detected based on a pulse signal from the rotation detecting sensor.
Japanese Patent Laid-Open Publication No. 6-280446 discloses a opening/closing control device that determines the occurrence of trapping when a drive speed and a drive acceleration of the motor is less than a predetermined value, which is determined based on a drive speed and a drive acceleration of the opening/closing member. The opening/closing control device detects the rotation of the motor by a motor position detecting sensor and calculates a motor rotation speed and a motor rotation acceleration. The opening/closing control device performs feedback/reverse control by comparing the motor rotation speed with a speed threshold value when a motor rotation speed change is regular. Alternatively, the opening/closing control device performs reverse control by comparing the motor rotation acceleration with an acceleration threshold value when the motor rotation speed change is not regular. At this time, the speed threshold value and the acceleration threshold value are corrected according to the drive voltage, the sliding resistance of the opening/closing member, and the like.
However, the following problem arises when the disclosed device is employed in a vehicle. Power is generally supplied to the opening/closing control device (for example, DC: 12V) from a battery in the vehicle. The voltage is thus fluctuated in response to a state of the load connected to the battery. If the motor for actuating the opening/closing member is driven by the battery which voltage is fluctuated, the motor speed is also fluctuated. In the method in which the speed of the motor having the fluctuated battery voltage is compared with a predetermined speed for the trapping detection, the wrong trapping detection may be caused by the fluctuation of the motor speed.
In order to prevent the wrong trapping detection due to the fluctuation of the motor speed, it is considered to lower a threshold value for determination (therefore the trapping is less determined). However, if the threshold value for determination is simply lowered, a longer time is required for actually detecting the trapping after the trapping occurrence. As a result, the, trapping detection is delayed and thus the load, which the trapped obstacle receives (trapping force), is increased. The reliability of the opening/closing control device may be lowered accordingly.
Thus, a need exists for a trapping detection device which detects the trapping accurately and improves the reliability thereof.